The key technique in difficult process
control is to make the control loop faster than the process. This
requires final element positioning of high dynamic response.
Hydraulic-electronic positioners have the basic high stiffness and precise and
rapid reversal capabilities which produce infinite resolution of valve position
with high frequency response. As a rule, the better these
characteristics, the faster and more precise the return to control after an
Particularly in refinery valves, very high
torques are needed to insure freedom from valve sticking. Hydraulic
drives are required to obtain these torques.
MORE REASONS WHY
HYDRAULICS ARE BETTER!
- Hydraulics are readily modulated or
controlled in both force and
- Hydraulics have very high efficiencies in
conversion of pressure to thrust.
- Hydraulics provide convenient energy storage
that can be used for high speed modulation or shutdown operations.
- Hydraulics operate over a wide range of
velocities and pressures.
- Maintenance costs of hydraulics are lower
as all moving parts
are submerged in hydraulic fluid and continually lubricated.
- Noise levels are dramatically reduced - no
air venting to atmosphere.
- No concern for wet air supply freezing in
- Size to force output ratio is much greater
than with pneumatics - hydraulic actuators are 75% smaller than
- Eliminate leakage with leak proof
components and connections using manifold construction and SAE Code
61 pipe and tube fittings.
- LVDT internally mounted to protect from
- No external moving pressure seals
- By using jet pipe servovalves, systems are
much more dirt tolerable than existing servo controlled hydraulic